Difficultly digestible saccharides have a difficultly digestible property, high water absorbing property, and swelling property and are used for controlling the ingestion amount of nutritional foods and it is reported that they are effective in accelerating digestion and excretion functions, the prophylaxis of diabetes mellitus, the inhibition of the absorption in the intestine of cholesterol and bile acids in foods, the reduction of lipids in blood serum, and the prophylaxis of carcinoma of the colon. Hence they are useful as dietary foods or dietary food additives.
In these difficultly digestible polysaccharides, glucomannan which is a polysaccharide derived from roots of plants is commercially available as a dietary food at present. However, not only glucomannan itself but also dietary food compositions containing more than 50% glucomannan cannot be granulated by conventional techniques owing to the characteristics specific to glucomannan, such as high water absorbing property, swelling property, and springiness and hence they are mainly commercially available as powdered foods.
The powdered foods, however, are objectionable because of taste and when such foods are ingested, the person may choke on the powder or the powder becomes unusually sticky in the mouth or sticks to the mouth. Consequently, there is a strong demand to obviate these objectionable features.
It was also found by the inventors' investigations that these difficulties in glucomannan also occurred in galactomannan, alginic acid, and various kinds of brans. However, in regard to various celluloses, pectin, and guar gum, insofar as difficultly digestible polysaccharides are concerned, there is known a method of granulating the polysaccharide after adding thereto an excipient such as lactose, starch, etc., and a binder such as gelatin, gum arabic, etc., and a method of gradually dissolving the polysaccharide in water and then forcibly granulating the aforesaid substances using a dual axle extruding granulator such as a screw type extruding granulator (Japanese Patent Laid Open (Kokai) No. 119,038/'79).
However, in the former method, there are such difficulties that the possible content of the difficultly digestible polysaccharide is greatly restricted and the resulting product is undesirable as a dietary food or dietary food additive in the point of containing other nutritional components. Hence its use as a food is also restricted. On the other hand, in the latter method, there are objections since a relatively forcible extruding granulator as compared to an ordinary extruding granulator (rotary type extruding granulator) is employed in the method. Thus, heat of friction is liable to be generated in the extrusion step causing a possibility of changing the properties of the product and when the granulation is continuously performed, clogging of basket holes and damage to the basket are liable to occur. Moreover, when glucomannan or other difficultly digestible polysaccharides showing the same tendency as glucomannan, such as galactomannan, alginic acid, various brans, etc., are present in an amount of more than 50% of the whole amount of the composition, it is very difficult to granulate the dietary composition with good reproducibility even by the foregoing granulation methods.